Design Of Beamline Optics Research Articles

Force-compensation-based adaptive thermal shape correction method for XFEL optics

With the successive development of free electron laser (FEL) facilities based on superconducting technology, the advance and diversity of beamline optical design have posed more stringent challenges to the controlling of thermal deformation for key optical elements. In this article, an adaptive thermal shape correction structure is presented, which converts the thermal stress into a bending moment to correct the mirror thermal bump by utilizing the difference in coefficient of thermal expansion (CTE) between materials, and the location relative to the mirror neutral plane. This moment is involved owing to the temperature rise derived from the FEL heat load, which has a certain adaptability to various thermal surface profile and can be precisely controlled by a chiller temperature regulation. In this work, we optimize the dimensions and position of the thermal shape correction blocks by analytical method and FEA simulation respectively. Eventually, this force-compensation-based adaptive scheme can achieve sub-nano sensitivity (∼ 0.1 nm) of mirror shape control, considering factors such as ease of engineering implementation and operational feasibility, even under repetition rates up to 100 kHz.

Modelling the power threshold and optimum thermal deformation of indirectly liquid-nitrogen cryo-cooled Si monochromators.

Maximizing the performance of crystal monochromators is a key aspect in the design of beamline optics for diffraction-limited synchrotron sources. Temperature and deformation of cryo-cooled crystals, illuminated by high-power beams of X-rays, can be estimated with a purely analytical model. The analysis is based on the thermal properties of cryo-cooled silicon crystals and the cooling geometry. Deformation amplitudes can be obtained, quickly and reliably. In this article the concept of threshold power conditions is introduced and defined analytically. The contribution of parameters such as liquid-nitrogen cooling efficiency, thermal contact conductance and interface contact area of the crystal with the cooling base is evaluated. The optimal crystal illumination and the base temperature are inferred, which help minimize the optics deformation. The model has been examined using finite-element analysis studies performed for several beamlines of the Diamond-II upgrade.

Integrated optical design method for the synchrotron radiation beamlines

In this paper, a new beamline optical system design method is reported in which the calculation of synchrotron radiation source flux distribution, monochromator spectral resolving power, mirror reflectance and grating diffraction efficiency are integrated together in one program to evaluate the whole beamline optical system performance. We demonstrate the advantage of this method by applying it to the Surface Physics beamline at Hefei Light Source to find out better optical system parameters. By using this method, a higher photon flux with the same spectral resolving power than the original design is achieved. The integrated optical system design method provides a great promising application in the beamline optical design and optimization in the future.

Tilting refractive x-ray lenses for fine-tuning of their focal length.

In this work, we measure and model tilted x-ray refractive lenses to investigate their effects on an x-ray beam. The modelling is benchmarked against at-wavelength metrology obtained with x-ray speckle vector tracking experiments (XSVT) at the BM05 beamline at the ESRF-EBS light source, showing very good agreement. This validation permits us to explore possible applications of tilted x-ray lenses in optical design. We conclude that while tilting 2D lenses does not seem interesting from the point of view of aberration-free focusing, tilting 1D lenses around their focusing direction can be used for smoothly fine-tuning their focal length. We demonstrate experimentally this continuous change in the apparent lens radius of curvature R: a reduction up to a factor of two and beyond is achieved and possible applications in beamline optical design are proposed.

Design of Beamline Optics for Large-Field Exposure

New mirror designs for an X-ray lithography (XRL) beamline have been devised for the large-field, high-power irradiation of wafers. In contrast to analytically described mirrors, such as toroids, ellipsoids, etc., the new shapes were numerically determined. The design method employed was developed by Xiao, et al. A beamline employing such an optimized mirror design should provide a high X-ray power density of 58 mW/cm2 over a 50-mm-square exposure area, and 88 mW/cm2 over a 40-mm-square exposure area, with a uniformity of better than ±2%. The slope error margin was also estimated using numerical simulations, and it was found that the exposure characteristics do not degrade when the slope error is less than 25 arcsecs over the whole surface of the mirror.

Design of beamline optics for EUVL.

The design of front-end collimating optics for extreme-ultraviolet lithography (EUVL) is reported. For EUVL, collimating optics consisting of a concave toroidal mirror and a convex toroidal mirror can achieve shorter optical path lengths than collimating optics consisting of two concave toroidal mirrors. Collimating optics consisting of a concave toroidal mirror and a convex toroidal mirror are discussed. The design of collimating optics for EUVL beamlines based on ray-tracing studies is described.

The BEPC focusing X-ray beamline optical design

A focusing X-ray beamline will be built at the Beijing 2.2–2.8 GeV electron-position collider (BEPC). This beamline is intended for diffraction, scattering and other applications. The beamline optical system consists of a right-angle structure monochromator with a laser encoder and a bent platinum coated cylindrical mirror which focuses the radiation with 1 to 1 magnification in the range of 3 to 12 keV. The diffraction and scattering experiments require stability of both the position and angle of the incident beam. Our beamline design incorporates beam monitors and stepping motor controlled motions of the focusing mirror to keep the beam focus point fixed when the electron orbit changes. Computer ray tracing has been done to check the image spot distortion caused by the offset adjustment to compensate the orbit change. The beamline design also has considerable flexibility for further development. As a Phase II plan, the monochromator will include a feedthrough structure to exchange crystals with a plane mirror-grating pair without a break in the vacuum. It will then be possible to extend the spectral range of the beamline of the soft X-ray range.

Time-resolved spectroscopy in synchrotron radiation

Synchrotron radiation (SR) from large-diameter storage rings has intrinsic time structure which facilitates time-resolved measurements from milliseconds to picoseconds and possibly below. The scientific importance of time-resolved measurements is steadily increasing as more and better techniques are discovered and applied to a wider variety of scientific problems. This paper presents a discussion of the importance of various parameters of the SR facility in providing for time-resolved spectroscopy experiments, including the role of beam-line optical design parameters. Special emphasis is placed on the requirements of extremely fast time-resolved experiments with which the effects of atomic vibrational or relaxational motion may be studied. Before discussing the state-of-the-art timing experiments, we review several types of time-resolved measurements which have now become routine: nanosecond-range fluorescence decay times, time-resolved emission and excitation spectroscopies, and various time-of-flight applications. These techniques all depend on a short SR pulse length and a long interpulse period, such as is provided by a large-diameter ring operating in a “single-bunch” mode. In most cases, the pulse shape and even the stability of the pulse shape is relatively unimportant as long as the pulse length is smaller than the risetime of the detection apparatus, typically 1 to 2 ns. For time resolution smaller than 1 ns, the requirements on the pulse shape become more stringent. Experiments requiring time resolution in the 10–100 ps range are conveniently done via observation of the phase shift of high harmonics of the storage-ring orbit frequency. Fast fluorescence decay time measurements and reflectance phase-change measurements have been done in this way. Because of the sensitivity of the harmonic amplitude to the pulse shape, these experiments require the SR pulse shape to stable. With the same phase-shift technique, measurements attaining time resolutions as small as 0.1 ps could be feasible if the SR pulse shape were made sufficiently stable. Observation of the shape of individual pulses of SR from the Stanford Positron Electron Accelerator Ring has been made under a variety of conditions using an Imacon 600 streak camera. These data are not completely analyzed at this time, but preliminary results are presented and discussed. Evidence is given of various modes of electron bunch-shape oscillation. These are apparently sensitive to beam current, kinetic energy, and accelerator cavity voltage.